The present invention relates generally to automotive fuel systems, and more particularly, to a returnless fuel system pressure valve with two-way parasitic flow orifice.
Conventional fuel injection systems utilize a fuel pump to provide fuel to a fuel rail that carries fuel to a plurality of fuel injectors. A pressure regulator is mounted in the fuel flow path so as to maintain the fuel pressure in the rail at approximately 40-psi greater than engine intake manifold vacuum. The pump, typically mounted in the fuel tank, runs at a constant speed and may deliver, for example, 90 liters per hour.
An Electronic Returnless Fuel System (ERFS) uses pulse width modulation (PWM) to control the voltage to the fuel pump in order to properly maintain a predetermined pressure differential across the fuel injectors. While PWM allows for improved fuel pump durability there can be an issue during low fuel flow requirements where limited voltage is supplied to the fuel pump. During a hot idle condition vapor lock may occur which prevents the fuel pump from delivering fuel to the engine. This vapor lock occurs because the low voltage being supplied to the fuel pump at an idle condition is not sufficient to drive the turbine at a high enough RPM to remove any vapor from the pumping chamber of the fuel pump.
Currently, ERFS applications use a Fuel Delivery Module (FDM) as their fuel pump sender assembly. The FDM includes a fuel storage container, as well as the fuel pump. A jet pump attached to the FDM takes a portion of the flow from the pump and uses that flow to keep the module filled. This allows the fuel pump to be surrounded by fuel at all times, thus improving low fuel-handling performance. An additional benefit of the jet pump is that it requires the fuel pump to output more flow to maintain both the flow requirements of the engine as well as the requirement of maintaining fuel within the module. The FDM typically includes a Parallel Pressure Relief Valve (PPRV). This valve contains a check valve and a relief valve in parallel with the check valve.
Certain ERFS applications use a pump and bracket assembly instead of an FDM. The pump and bracket assembly does not contain the PPRV or a jet pump. Fuel out of the pump is delivered directly to the engine. The lack of a jet pump has led to a change to the PPRV for the pump and bracket ERFS applications to prevent possible vapor lock conditions. The change involves an addition of a fixed orifice bleed port on the check valve side of the PPRV. This orifice, depending on the size, bleeds off a certain amount of fuel similar to the jet pump on the FDM.
Typical flows out of the orifice, to help prevent vapor lock at hot idle conditions, have been around 15-20 LPH. With the fixed orifice, this amount of flow will bleed back into the fuel tank not only at idle (where it is needed) but at wide-open throttle (WOT) as well. Unfortunately, this additional flow must be accounted for when sizing a fuel pump for an ERFS application and results in using a larger and more costly pump than required during non-idle conditions.
The disadvantages associated with these conventional returnless fuel delivery techniques have made it apparent that a new technique for returnless fuel delivery is needed. The new technique should prevent vapor lock and should not require fuel pump oversizing for non-idle conditions. The present invention is directed to these ends.
It is, therefore, an object of the invention to provide an improved and reliable returnless fuel system pressure valve with two-way parasitic flow orifice. Another object of the invention is to prevent vapor lock conditions while not requiring fuel pump oversizing for non-idle conditions.
In accordance with the objects of this invention, a returnless fuel system pressure valve with two-way parasitic flow orifice is provided. In one embodiment of the invention, a fuel system pressure valve is interposed in a fuel line between a fuel pump and a fuel rail for controlling fuel flow from the pump to the rail and from the rail to the pump. The valve includes a valve housing having a pair of half sections to form a valve chamber. A check valve is mounted in the chamber and is operable to allow fuel flow from the pump to the fuel line upon the fuel pump delivering a predetermined fuel pressure to the fuel line. A pressure relief valve is mounted within the chamber parallel to the check valve and is operable to allow fuel in the fuel line to flow through the housing to the fuel pump upon fuel pressure in the fuel line exceeding a predetermined relief pressure. In addition, a parasitic flow orifice is mounted in fluid communication with the valve chamber and allows fuel in the valve chamber to flow through the orifice to a fuel tank when valve chamber pressure is below a predetermined valve chamber pressure. Fuel is prevented from flowing through the parasitic flow orifice when the valve chamber pressure exceeds the predetermined valve chamber pressure.
The present invention thus achieves an improved returnless fuel system pressure valve with two-way parasitic flow orifice. The present invention is advantageous in that it prevents vapor lock during idle conditions by allowing parasitic fuel flow, but does not require an oversized fuel pump because parasitic fuel flow is prevented for non-idle conditions.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.